Project Summary Title: Mechanisms of neuroinflammation in brain metastasis progression Despite significant progress in early cancer screening and treatment regimens for primary tumors, the overall mortality of patients with metastatic relapse has not improved in the past two decades. Many sites of metastatic relapse are commonly diagnosed in the clinic, but brain metastasis is the most devastating with a median survival of fewer than six months. Thriving in a sanctuary protected by the blood-brain barrier (BBB), brain metastases are shielded from most anti-cancer drugs. As a result, the incidence of brain metastasis is increasing, despite increasing control of primary tumors. Thus, to reduce cancer mortality, rationally designed therapeutics, based on a mechanistic understanding of metastasis in the context of the unique brain microenvironment, are urgently needed for brain metastasis patients. The immune system has indisputable and ubiquitous roles in regulating both primary tumors and metastases. Traditionally viewed as immunoprivileged organ, the role of neuroinflammation in brain tumor progression is largely underexplored. In this proposed study, we will use transgenic mouse models and state-of-the-art genomics and imaging approach to trace and analyze the role of highly heterogeneous cell types involved in neuroinflammation and their roles in regulating brain metastatic outgrowth. This collaborative effort from a multidisciplinary team, including a cancer biologist, an expert in neuroinflammation, a computational biologist and a bioinformatician and will allow us to: 1) dissect distinct contribution subpopulation of myeloid cells in regulating brain metastasis at phenotypical level (Aim 1); 2) visualize and quantitatively measure the behavior of brain microenvironmental niche and transcriptome heterogeneity of inflammatory myeloid cell that that nurtures metastasis in brain (Aim 2). 3) Targeting pro-inflammatory myeloid cells as means of brain metastasis prevention. Shifting the current clinical treatment model relies on new in-depth mechanistic insights obtained through basic and pre-clinical innovative research. Utilizing cutting-edge sequencing and imaging modality coupled with classic transgenetic models and clinical tissue samples, we now have the unprecedented capacity to systematically dissect the traits of metastatic behavior and discover potential novel therapeutic targets for paradigm-shifting novel adjuvant therapy for brain metastasis patients.